Extendable support column

ABSTRACT

A hydropneumatic support column for a table top or the like has a cylinder, a two-part piston in the cylinder and a piston rod extending outwardly of the cylinder. Respective axial faces of the two piston parts conformingly engage axially spaced portions of the inner cylinder wall, and spacedly opposite radial walls of the piston parts bound a receptacle for an O-ring dimensioned to define a gap with the inner cylinder wall in the relaxed position. The inner end of the piston rod threadedly engages one piston part and abuttingly engages the other so that the resilient O-ring may be axially compressed between the radial walls of the piston parts by turning the external portion of the piston rod until it closes the gap, thereby breaking communication between two axial grooves in the piston parts which jointly connect the two compartments on opposite sides of the piston when the gap is open.

United States Patent Continuation-impart of application Ser. No.707,846, Feb. 23, 1968, now Patent No. 3,503,472. This application Feb.17, 1970, Ser. No. 11,946

EXTENDABLE SUPPORT COLUMN 9 Claims, 2 Drawing Figs.

[1.8. Ci 188/300, 188/316, 248/354 l-l int. Cl F1611 63/00 Field ofSearch... 188/271 [56] References Cited UNITED STATES PATENTS 3,376,9574/1968 Baumgartner 188/316 Primary Examiner-George E. A. HalvosaA1t0meyl(elman and Berman ABSTRACT: A hydropneumatic support column fora table top or the like has a cylinder, a two-part piston in thecylinder and a piston rod extending outwardly of the cylinder.Respective axial faces of the two piston parts conformingly engageaxially spaced portions of the inner cylinder wall, and spacedlyopposite radial walls of the piston parts bound a receptacle for anO-ring dimensioned to define a gap with the inner cylinder wall in therelaxed position. The inner end of the piston rod threadedly engages onepiston part and abuttingly engages the other so that the resilientO-ring may be axially compressed between the radial walls of the pistonparts by turning the external portion of the piston rod until it closesthe gap, thereby breaking communication between two axial grooves in thepiston parts which jointly connect the two compartments on oppositesides ofthe piston when the gap is open.

EXTENDABLIE SUPPORT COLUMN This application is a continuation-in-part ofmy copending application, Ser. No. 707,846, filed on Feb. 23, 1968, nowUS. Pat. No. 3,503,472.

This invention relates to support columns of adjustable length, andparticularly to extendable columns in which a piston is axially movablein a sealed, fluid-filled cylinder and axially divides the cylindercavity into two compartments. A piston rod extends from the pistonaxially outward of the cylinder. The cylinder and piston rod areinterposed between the object to be supported and the ground or floor.The axial length of the column can be changed only when the twocompanments are connected through a valved bypass duct.

Columns of the type described depend for operativeness on a tight sealbetween the piston and the inner wall of the cylinder. Even a slightleak between piston and cylinder wall causes the column to change inlength under an applied load or under internal pressure whicheverprevails.

It has therefore been common practice heretofore to provide the pistonwith at least one sealing ring of resilient material whose outerdiameter in the relaxed condition is greater than the inner diameter ofthe cylinder so that the ring is strongly stressed in compression at alltimes. The resulting contact pressure between the ring and the cylinderwall causes considerable friction.

The known columns employing resilient sealing rings on the pistoninherently have limited transverse rigidity when extended. When a majorportion of the piston rod projects from the cylinder, good transverserigidity of the column requires precise guiding of the rod in a radialend wall of the cylinder and by the piston. If the radial position ofthe piston is determined by a resilient sealing ring, the longitudinalaxis of the rod is not held parallel to the cylinder axis withsufficient precision to prevent bending stresses to be generated in thecolumn by an applied load. Such stresses cause rapid deterioration ofthe seals at the two guiding points of the rod and premature failure ofthe column.

If the column is filled partly with liquid and partly with a gas under apressure sufficiently higher than atmospheric pressure, the columnexpands spontaneously when relieved of an external load as soon as thebypass duct is opened. The internal gas pressure required depends to asignificant extent on the friction between the piston and the cylinderwall. An interposed, strongly compressed sealing ring requires thecolumn to be operated under a much higher gas pressure than wouldotherwise be needed, and all other features of the column must beadjusted to the higher operating pressure.

The hydropneumatic columns referred to are normally shortened bymanually pushing the piston rod inward of the cylinder against thepressure of the gas. The force required for reducing the length of thecolumn is greatly increased by high friction between a sealing ring onthe piston and the inner cylinder wall, and is additionally increased bythe need for operating at relatively high internal gas pressure asdescribed in the preceding paragraph.

The useful life of a column of the type described is mainly determinedby the wear of the sealing ring. Some such columns are lengthened andshortened relatively frequently, as in a table which may serve as adining table when supported by fully extended columns, and as a coffeetable when supported on the same columns reduced to their minimumlength. The contact pressure between the sealing ring and the innercylinder wall during their relative sliding movement is a major factorin determining the rate of wear of the ring. The greater the pressure,the shorter the useful life of the sealing ring under otherwiseidentical conditions.

The primary object of the invention is the provision of a column of thetype described in which the contact pressure between a sealing member onthe piston and the inner wall of the cylinder is insignificant while thelength of the column is being changed, whereby the aforementionedshortcomings of the known extendable columns are avoided.

Another object is the provision of a column of the type described whichis simple in its design, has few and rugged parts, yet is reliable inits operation and of high rigidity.

With these and other objects in view, the invention, in one of itsaspects, resides in a column having a two-part piston. The two pistonmembers have respective axial faces which conformingly engage twoaxially spaced portions of the inner cylinder face, and respectiveradially extending faces spaced opposite each other so as axially tobound a receptacle therebetween. The axial walls of the receptacle areprovided by the inner cylinder face and one of the piston members. Eachpiston member is formed with a conduit having an orifree in thereceptacle and an orifice in one of the two compartments into which thecylinder cavity is divided by the piston.

A terminal portion of the piston rod in the cylinder cavity threadedlyengages one of the piston members and is connected with the other,exterior terminal portion of the piston rod for joint angular movementin respective planes perpendicular to the cylinder axis, and usuallyabout the cylinder axis. An abutment on the inner piston rod end movesthe other piston member inwardly of the aforementioned receptacle towardthe threadedly engaged piston member when the exterior piston rod end isturned.

A resilient member interposed between the radial faces of the pistonmembers in the receptacle is dimensioned so as to define a gap with oneof the axial receptacle walls when in the relaxed condition, the gapconnecting the orifices of the two conduits in the receptacle. Whencompressed between the radial piston faces, the resilient member engagesthe last-mentioned axial wall and thereby closes the gap and preventsflow of fluid between the cylinder compartments.

Other features, additional objects and many of the attendant advantagesof this invention will readily be appreciated as the same becomes betterunderstood by reference to the following detailed description ofpreferred embodiments when considered in connection with theaccompanying drawing, in which:

FIG. 1 shows a hydropneumatic support column of the invention in axialsection, its bypass duct being open; and

FIG. 2 shows a portion of the column of FIG. 11 on a larger scale.

Referring now to the drawing in detail, and initially to FIG. 1, thereis seen a hollow cylinder ll whose axial ends are sealed respectively byan imperforate plug la provided with a blind, radial, threaded bore lb,and by an annular plug lc slidably receiving a piston rod 11. Theportion of the piston rod projecting from the plug 10 is provided with aradial threaded bore 11a. The bores lb and 11a may be used for attachingthe piston rod 11 to a base and the cylinder 1 to a table top which isto be supported at an adjustable height by the illustrated column.

A two-part piston 2 attached to the piston rod 11 divides the cylindercavity into two compartments 118, 19 whose capacity varies during axialmovement of the piston. The lower compartment l9 and an axial portion ofthe upper compartment 18 near the piston are filled with liquid, whilethe remainder of the compartment is occupied by a cushion of compressedair.

As is better seen in FIG. 2, piston member 3, 4 is a tube whose bore isprovided with threads 5 over much of its length. The upper axial portion3 of the piston member has an outer face which confonningly engages theuniformly cylindrical inner face of the cylinder 1 with a sliding fit.The lower axial portion 41 of the piston member also has a cylindricalouter face but of reduced diameter. The other piston member 8 is a shortcylindrical tube which slidably receives the reduced portion 4 of thepiston member in its bore and whose outer axial face conforms to theinner cylinder face.

Spacedly opposite radial faces of the two piston members axially boundan annular receptacle M which is bounded radially by the outer face ofthe reduced piston member portion 4 and by the inner cylinder face. AnO-ring 9 of resilient rubber or plastic composition is received in thereceptacle 14, its dimensions being chosen so that it radially defines agap with the inner cylinder face when in the illustrated relaxedcondition in which the ring is substantially tore-shaped. Axial grooves23 in the otherwise smoothly cylindrical, outer face of the pistonportion 3 have orifices in the compartment 18 and in the receptacle ofthe ring 9 so as to provide a conduit for fluid flow between thecompartment 18 and the gap between the ring 9 and the cylinder 1. Thepiston member 8 is formed with a corresponding conduit formed by grooves24 having orifices in the compartment 19 and in the gap between the ring9 and the cylinder 1.

The upper or interior terminal portion of the piston rod 11 is a plug 7which threadedly engages the threads 5 in the bore of the piston member3, 4. A portion of the plug 7 downwardly projects from the bore of thepiston member 3, 4 and has an integral collar 6 which abuttingly engagesthe radial face of the piston member 8 remote from the O-ring 9 underall normal operating conditions. A downwardly open bore of the plug 7receives the smoothly cylindrical portion of the piston rod 11, relativeangular movement in a plane perpendicular to the cylinder axis beingprevented by a transverse pin 10 which passes radially through bothpiston rod portions, the connection being axially secured by a ring 12of spring wire received simultaneously in circumferential grooves ofboth portions. A rubber ring 13 on the cylindrical piston rod portioncontiguously adjacent the plug 7 cushions the impact of the plug 7 andof the attached piston against the plug 10 during outward travel of thepiston rod 11. Axial downward movement of the plug 7 from the positionshown in FIG. 2 is prevented by a snap ring 21 on the plug 7 engagingthe piston portion 3 and thus avoiding disengagement of the piston rodfrom the piston.

In the illustrated condition of the piston 2, the two compartments l8,l9 communicate with each other through the throttling passage providedby the conduits 23, 24. Depending on the magnitudes of an appliedexternal load and of the gas pressure of the air cushion, the piston 2and piston rod 11 may be in equilibrium in the illustrated position.They can readily be shifted by increasing or decreasing the externalload.

When it is desired to fix the length of the column, the outer terminalportion of the piston rod 11 is turned relative to the cylinder 1 aboutthe cylinder axis to shift the plug upwardly on the threads 5. Suchturning may be facilitated by inserting threaded, straight rods in thebores lb, 110. Friction between the piston 2 and the inner wall of thecylinder 1 is normally sufficient for initially impeding rotation of thepiston, but the piston portion 3 and the inner cylinder face may beprovided with engaged, axial ribs and grooves if so desired, as is shownin the aforementioned copending application.

As the collar 6 approaches the reduced portion 4 of the threaded pistonmember, the Oring 9 is axially compressed between the opposite radialfaces of the two piston members as the piston member 8 moves inwardly ofthe receptacle 14. The O-ring correspondingly expands in a radialdirection until it closes the gap near the cylinder face shown in FIG.2, thereby interrupting communication between the compartments l8, 19.

The ring 9 is protected against damage under excessive axial pressure byabutting engagement of the collar 6 with the reduced piston portion 4.As soon as the O-ring 9 engages the cylinder face, it makes relativeangular movement of the piston 2 and the cylinder I practicallyimpossible even in the absence of engaged ribs and grooves. There isvery little, if any, relative movement of the ring and cylinder whilethey are frictionally engaged, and wear of the ring 9 is nominal.

FIG. 2 is drawn substantially to scale. It shows that the overall axiallength of the piston 2, as measured over the outer faces of the pistonmembers 3, 4 and 8 which engage the inner cylinder face, issubstantially greater than the piston or cylinder radius, and actuallygreater than three quarters of the piston diameter even when the pistonmember 8 moves to the limit of its stroke inwardly of the receptacle 14.The clearance required between the piston 2 and the cylinder 1 is toosmall to permit realistic representation on the scale of FIG. 2. Thepiston 2 is therefore precisely guided in the cylinder 1 in alloperating conditions of the apparatus, and the transverse rigidity ofthe device under stresses unable to deform the metallic parts isdetermined by the seal in the plug lc which may be made relatively rigidin a known manner, partly illustrated.

LII

The cylinder-engaging face of the thickest and correspondingly rigid,metallic piston portion 3 extends over approximately one-half of theaxial length of the piston, thereby preventing deformation of the pistoneven under very high bending stresses applied to the column, and backingthe metallic cylinder to protect the latter against distortion. Thegrooves 23 are about as wide circumferentially as they are shown to bedeep radially, and too few in number, typically three, offset to reducethe backing of the cylinder 1 by the piston 2 to a significant extent.

The aforedescribed extendable support column is simple and consists ofrelatively few parts because the O-ring 9 operates both as a valve whichmay be opened and closed from the outside for shifting or fixing thepiston 2, and as a seal which prevents leakage between the compartmentsl8, 19 in the closed valve position.

The piston 2 provides precise radial guidance for the piston rod 11 andis movable in the cylinder 1 with very little friction if it is desiredto change the column length. The column may therefore be provided withan air cushion of relatively low pressure which simplifies theconstruction, operation and maintenance of the column.

Obviously, many changes may be made in the illustrated embodimentwithout departing from the spirit and scope of the invention. Whileexternal grooves 23,24 have been chosen as conduits for connecting thecompartments l8, 19 for the convenience with which such conduits aremachined in the piston members 3, 8, other conduits may be formed in thepiston members, and their orifices in the receptacle 14 need notnecessarily be located near the inner cylinder face if the dimensions ofthe relaxed O-ring 9 are chosen to open a gap axially along the pistonportion 4.

Other modifications will readily suggest themselves to those skilled inthe art, and it should be understood that the invention is not limitedto the example chosen for the purpose of the disclosure, but is to beconstrued broadly and limited solely by the scope of the appendedclaims.

What is claimed is:

I. An extendable support column comprising, in combination:

a. a cylinder member having an axis and an inner face of uniform crosssection transversely of said axis, said face bounding a cavity in saidcylinder member;

b. sealing means sealing said cavity from the ambient atmosphere;

c. piston means axially movable in said cavity and dividing the sameinto two compartments varying in their capacity during axial movement ofsaid piston means,

1. said piston means including two piston members having respectiveaxial faces conformingly engaging two axially spaced portions of saidinner face and respective radially extending faces spacedly oppositeeach other and axially bounding a receptacle therebetween, the axialwalls of said receptacle being constituted by said inner face and one ofsaid piston members,

2. each piston member being formed with a conduit having an orifice insaid receptacle and one of said compartments;

d. a piston rod axially movable relative to said cylinder member andhaving a first terminal portion axially projecting from said cylindermember and a second terminal portion in said cavity threadedly engagingone of said piston members, said terminal portions being connected forjoint angular movement in respective planes transverse to said axis;

. abutment means on said second terminal portion engageable with theother piston member for moving the other piston member inwardly of saidreceptacle toward said one piston member when said first terminalportion is turned relative to said one piston member;

a resilient member interposed between said radially extending faces andsaid axial walls in said receptacle, said resilient member beingdimensioned l. to define a gap with one of said axial walls when in therelaxed condition, the gap connecting the orifices of said conduits insaid receptacle, and

2. to engage said wall and thereby to close said gap when compressedbetween said radially extending faces during movement of said otherpiston member inwardly of said receptacle; and

g. a fluid filling said compartments, said recesses and said gap.

2. A column as set forth in claim 1, wherein said one piston member hasa radially reduced portion, said other piston member being annular andslidably receiving said reduced portion therein.

3. A column as set forth in claim 1, wherein said axial faces of saidpiston members are formed with respective grooves open toward said innerface, said grooves constituting said conduits, said one axial wall ofsaid receptacle being said inner face.

4. A column as set forth in claim 1, wherein said receptacle and saidresilient member are annular about said axis.

5. A column as set forth in claim 4!, wherein said resilient member issubstantially tore-shaped when in said relaxed condition.

6. A column as set forth in claim 1, wherein the overall axial length ofsaid piston means, as measured over said axial faces of said pistonmembers, is at least equal to the radius of said inner face.

7. A column as set forth in claim 6, wherein the axial length of one ofsaid axial faces is approximately equal to and not substantially smallerthan one-half of said axial length of said piston means.

8. A column as set forth in claim 7, wherein said one axial face is saidaxial face of said one piston member.

9. A column as set forth in claim 8, wherein said one piston member hasa radially reduced portion axially offset from said axial face thereof,said other piston member being annular and having a bore slidablyreceiving said reduced portion in conforming engagement.

1. An extendable support column comprising, in combination: a. acylinder member having an axis and an inner face of uniform crosssection transversely of said axis, said face bounding a cavity in saidcylinder member; b. sealing means sealing said cavity from the ambientatmosphere; c. piston means axially movable in said cavity and dividingthe same into two compartments varying in their capacity during axialmovement of said piston means,
 1. said piston means including two pistonmembers having respective axial faces conformingly engaging two axiallyspaced portions of said inner face and respective radially extendingfaces spacedly opposite each other and axially bounding a receptacletherebetween, the axial walls of said receptacle being constituted bysaid inner face and one of said piston members,
 2. each piston memberbeing formed with a conduit having an orifice in said receptacle and oneof said compartments; d. a piston rod axially movable relative to saidcylinder member and having a first terminal portion axially projectingfrom said cylinder member and a second terminal portion in said cavitythreadedly engaging one of said piston members, said terminal portionsbeing connected for joint angular movement in respective planestransverse to said axis; e. abutment means on said second terminalportion engageable with the other piston member for moving the otherpiston member inwardly of said receptacle toward said one piston memberwhen said first terminal portion is turned relative to said one pistonmember; f. a resilient member interposed between said radially extendingfaces and said axial walls in said receptacle, said resilient memberbeing dimensioned
 1. to define a gap with one of said axial walls whenin the relaxed condition, the gap connecting the orifices of saidconduits in said receptacle, and
 2. to engage said wall and thereby toclose said gap when compressed between said radially extending facesduring movement of said other piston member inwardly of said receptacle;and g. a fluid filling said compartments, said recesses and said gap. 2.each piston member being formed with a conduit having an orifice in saidreceptacle and one of said compartments; d. a piston rod axially movablerelative to said cylinder member and having a first terminal portionaxially projecting from said cylinder member and a second terminalportion in said cavity threadedly engaging one of said piston members,said terminal portions being connected for joint angular movement inrespective planes transverse to said axis; e. abutment means on saidsecond terminal portion engageable with the other piston member formoving the other piston member inwardly of said receptacle toward saidone piston member when said first terminal portion is turned relative tosaid one piston member; f. a resilient member interposed between saidradially extending faces and said axial walls in said receptacle, saidresilient member being dimensioned
 2. to engage said wall and thereby toclose said gap when compressed between said radially extending facesduring movement of said other piston member inwardly of said receptacle;and g. a fluid filling said compartments, said recesses and said gap. 2.A column as set forth in claim 1, wherein said one piston member has aradially reduced portion, said other piston member being annular andslidably receiving said reduced portion therein.
 3. A column as setforth in claim 1, wherein said axial faces of said piston members areformed with respective grooves open toward said inner face, said groovesconstituting said conduits, said one axial wall of said receptacle beingsaid inner face.
 4. A column as set forth in claim 1, wherein saidreceptacle and said resilient member are annular about said axis.
 5. Acolumn as set forth in claim 4, wherein said resilient member issubstantially tore-shaped when in said relaxed condition.
 6. A column asset forth in claim 1, wherein the overall axial length of said pistonmeans, as measured over said axial faces of said piston members, is atleast equal to the radius of said inner face.
 7. A column as set forthin claim 6, wherein the axial length of one of said axial faces isapproximately equal to and not substantially smaller than one-half ofsaid axial length of said piston means.
 8. A column as set forth inclaim 7, wherein said one axial face is said axial face of said onepiston member.
 9. A column as set forth in claim 8, wherein said onepiston member has a radially reduced portion axially offset from saidaxial face thereof, said other piston member being annular and having abore slidably receiving said reduced portion in conforming engagement.